Contributed by Kotaro Sasaki, MD, Sheldon I. Bastacky, MD, Anil V. Parwani, MD. PhD and Debra L. Zynger, MD
A 62 year-old man presented to his primary care physician with an unexplained 60 lb weight loss, slight nausea and anorexia over the course of a year. A dynamic, contrast-enhanced abdominal computed tomography scan revealed an incidental 1.8 cm enhancing mass at the lower pole of the left kidney with no other abnormalities identified. Laparoscopic partial nephrectomy of the tumor was performed and the patient made an uneventful recovery. The tumor has followed a benign course without evidence of local recurrence or metastasis during the follow-up period of 2 months.
The gross specimen consisted of two focally cauterized fragments of kidney containing a well-circumscribed, partially cystic tan lesion measuring 1.8 cm in maximum diameter.
Microscopic examination showed a cellular tumor with a solid growth pattern and focal myxoid change. Numerous vessels of varying size, some with hemangiopericytoma-like configuration, were dispersed throughout the tumor (Fig. 1). The tumor cells were small, round to oval, with smooth nuclear contours, vesicular chromatin, occasional single visible nucleoli, and a moderate amount of pale eosinophilic cytoplasm (Fig. 1). Atypia was minimal to absent and no mitotic figures or necrosis were seen. Surgical margins were free of tumor.
An extensive immunohistochemical panel was performed to evaluate the tumor (Table 1, Fig. 2).